1. Field of the Invention
This invention generally relates to methods and apparatus for bone resection to allow for the interconnection or attachment of various prosthetic devices with respect to the patient. More particularly, the present invention relates to the use of a wireplasty bone resection technique in which wires or cables act as bone cutting tools.
2. Background Art
Different methods and apparatus have been developed in the past to enable a surgeon to remove bony material to create specifically shaped surfaces in or on a bone for various reasons including to allow for attachment of various devices or objects to the bone. Keeping in mind that the ultimate goal of any surgical procedure is to restore the body to normal function, it is critical that the quality and orientation of the cut, as well as the quality of fixation, and the location and orientation of objects or devices attached to the bone, is sufficient to ensure proper healing of the body, as well as appropriate mechanical function of the musculoskeletal structure.
In total knee replacements, for example, a series of planar and/or curvilinear surfaces, or “resections,” are created to allow for the attachment of prosthetic or other devices to the femur, tibia and/or patella. In the case of the femur, it is common to use the central axis of the femur, the posterior and distal femoral condyles, and/or the anterior distal femoral cortex as guides to determine the location and orientation of distal femoral resections. The location and orientation of these resections are critical in that they dictate the final location and orientation of the distal femoral implant. It is commonly thought that the location and orientation of the distal femoral implant are critical factors in the success or failure of the artificial knee joint. Additionally, with any surgical procedure, time is critical, and methods and apparatus that can save operating room time, are valuable. Past efforts have not been successful in consistently and/or properly locating and orienting distal femoral resections in a quick and efficient manner.
The use of oscillating saw blade based resection systems has been the standard in total knee replacement and other forms of bone resection for over 30 years. Unfortunately, present approaches to using such planar saw blade instrumentation systems all possess certain limitations and liabilities.
Perhaps the most critical factor in the clinical success of any bone resection for the purpose of creating an implant surface on the bone is the accuracy of the implant's placement. This can be described by the degrees of freedom associated with each implant. In the case of a total knee arthroplasty (TKA), for example, for the femoral component these include location and orientation that may be described as Varus-Valgus Alignment, Rotational Alignment, Flexion-Extension Alignment, A-P location, Distal Resection Depth Location, and Mediolateral Location. Conventional instrumentation very often relies on the placement of ⅛ or 3/16 inch diameter pin or drill placement in the anterior or distal faces of the femur for placement of cutting guides. In the case of posterior referencing systems for TKA, the distal resection cutting guide is positioned by drilling two long drill bits into the anterior cortex along the longitudinal axis of the bone. As these long drills contact the oblique surface of the femur they very often deflect, following the path of least resistance into the bone. As the alignment guides are disconnected from these cutting guides, the drill pins will “spring” to whatever position was dictated by their deflected course thus changing their designated, desired alignment to something less predictable and/or desirable. This kind of error is further compounded by the “tolerance stacking,” inherent in the use of multiple alignment guides and cutting guides.
Another error inherent in these systems further adding to mal-alignment is deflection of the oscillating saw blade during the cutting process. The use of an oscillating saw blade is very skill intensive as the blade will also follow the path of least resistance through the bone and deflect in a manner creating variations in the cut surfaces which further contribute to prosthesis mal-alignment as well as poor fit between the prosthesis and the resection surfaces. Despite the fact that the oscillating saw has been used in TKA and other bone resection procedures for more than 30 years, there are still reports of incidences where poor cuts result in significant gaps in the fit between the implant and the bone. The safety of these saws is also questionable as minor incidences of misuse can result in serious harm and disability.
While oscillating saws have been the preferred tools for performing bone resections as part of an implantation procedure, other forms of bone saws and cutting instruments have also been used to cut bones. Generally, the problems of precision, accuracy and safety of these other cutting instruments are even greater than with an oscillating saw. U.S. Pat. No. 5,725,530 describes a planar surgical saw that utilizes a dual chain saw arrangement with guards along the outer sides of the chain saw blades. A surgeon's gigli saw, for example, has a cutting wire with a handle on each end that is wrapped around a bone to be cut. The surgeon alternates pulling each handle to run the cutting wire back and forth around the bone to cut the bone. U.S. Pat. No. 4,709,699 describes an improved cutting wire for a surgeon's gigli saw. U.S. Pat. No. 6,368,353 describes the use of a gigli saw for resecting the neck of the humerous bone as part of an implant procedure for a shoulder prosthesis. Although conventional chain saws and gigli saws can be very efficient general purpose cutting tools, these saws have little ability to be guided and aligned so as to make the precise and accurate resection cuts required for effective implants.
Improvements in the precision, accuracy, and safety of tools for resecting bone surfaces are desired in order to increase the efficacy of orthopedic procedures and enable the surgeon to better achieve the benefits of a standard, less invasive, and more efficacious joint reconstruction.